1. Geological Faults

2. Objective: By the end of this
session you should be able to use
diagrams and examples to
describe and explain the different
types of geological faults

3. Types of Geological Faults
Vertical Movement (Dip-Slip)
• Normal (East African Rift Valley)
• Reverse (Salt Lake City)
Horizontal Movement (Strike-Slip)
• Tear Faults (The Great Glen Scotland)
• Transform Faults (San Andreas Fault)
Thrust Faults
• Overfold or Nappe (cliffs Broadhaven
Dyfed)

4. You have one minute to draw and label
a normal fault

5. Normal Faults
TENSION / Pulling motion = LENGTHENING
H
Throw = Vertical Displacement
T Heave = Horizontal Displacement
Fault
Scarp
Fault Plane

6. Upthrow and Downthrow
Give five ways that the blocks could
have moved?
A
UPTHROW
B
DOWNTHROW
1. A moved up while B moved down
2.
3.
4.
5.
Throw is therefore a RELATIVE position

7. Reverse Faults
COMPRESSION / Pushing motion = SHORTENING
T
H
Fault Plane

8. Rift Valleys
Fault Scarp
Graben or Rift Valleys are the result of subsidence between Normal Faults
(i.e. TENSION/pulling) Horsts are left upstanding after subsidence on either side.
Name a famous rift valley:________________________________________

9. Strike-slip faults (horizontal faults)
• Tear Faults - the result of shearing forces applied to
rocks this can be famously seen at the Great Glen
Fault where there is SINISTRAL movement (to the
left) of a Granite Intrusion split in two. The opposite
of sinistral movement is DEXTRAL movement (to the
r_____).

10. Strike-slip faults (horizontal faults)
• Transform Faults - associated with plate
margins. Famously seen at the S___ A____
Fault. These faults are also common at right
angles to a mid-ocean ridge. Plate motion can
also be seen at transform faults.

11. Thrust Faults
• Intense c__________
•Beds so contorted movement can only
occur through fracture
Nappe
•Overfold or Nappe moves up and over
lower part
•A type of reverse fault with an almost
horizontal fault plane
•Crustal s_________ takes place
•Associated with mountain building
•Older rocks can be pushed over y_____
rocks
•At the Moine Thrust Fault in NW Scotland
Pre-Cambrian rocks are found above
Cambrian rocks

12. Other Fault Features
• Fault Breccia: crushed and broken fragments along
fault planes
• Slickenslides: deep grooves along fault planes
showing direction of movement
• Gaps along fault planes: often filled with fluids such
as magma giving rise to dykes or hydrothermal
solutions carrying minerals (such as veins of galena
and fluorite found in the Pennines)
• Erosion: valleys can form along weak fault lines;
upthrow can be eroded to the same level as
downthrow which can leave misleading geological
patterns

13. What have you remembered?
(Blank paper, two minutes!!!)
1. Draw and label a Dip-Slip Fault
2. Name a specific example of a Normal
Fault
3. Is dextral movement to the left or
right?
4. What types of faults involve Nappes?

14. What have you remembered?

15. Exam Question from Summer 2007

16. Mark Scheme for Exam Question
• Specific type of fold/fault e.g. "reverse
fault", "anticline" (1)
• Quality of diagram/description (2)
• Reference to appropriate scale (1)
• Specific location of feature (1)
• Correct name of stress involved (1) R
• e.g. Extension/Tension for normal fault,
• Compression for reverse/thrust fault or fold
• Shear for tear fault